1. Field of the Invention
This invention relates generally to the field of rigid disc drive data storage devices, and more specifically, but not by way of limitation, to a mechanism which contributes to the even distribution of clamping force by the disc clamp used to mount the discs to the spindle motor in a rigid disc drive data storage device.
2. Brief Description of the Prior Art
Rigid disc drive data storage devices--or disc drives--of the type known as "Winchester" disc drives are well known in the industry. In such disc drives, one or more rigid discs, coated with a magnetizable medium, are mounted for rotation at a constant high speed on a spindle motor. An array of heads--typically one per disc surface--is mounted for controllable motion to an actuator which moves the heads across the surfaces of the discs to any desired one of a plurality of circular, concentric data tracks. These heads are used to record--or write--and retrieve--or read--data on the recording medium, and include a self-acting hydrodynamic air bearing surface which cooperates with a thin layer of air dragged along by the spinning discs to fly the heads slightly above the disc surfaces.
In early disc drives of this type manufactured in the 51/4 inch form factor, the data tracks on the disc surfaces were distributed on the disc surfaces at a radial track density of only 300-400 tracks per inch (tpi), and the heads were designed to fly approximately 12-14 inches above the disc surfaces. Market demands for smaller form factors and increased data capacity have lead to current disc drive products with track densities in the range of 1800-2600 tpi, and head flying heights of only 2.5-4.0 inches.
The technological advances which have lead to the current families of products in the 21/2 inch and smaller form factors have included improved heads, media, actuators and systems for controlling the movement of the heads between tracks.
The need to provide the maximum amount of storage capacity--and thus the maximum number of discs--in these small form factors has lead to the use of aluminum discs which are only 0.025 inches thick, and the expected use of canasite discs only 0.015 inches thick. Furthermore, since these types of disc drives are intended for use in laptop and notebook types of computer systems, they are expected to withstand mechanical shocks in the range of 150-300 Gs. In order to meet such rigorous shock specifications, the clamping force used to secure the discs to the spindle motor must be on the order of 100-120 lb.
A typical type of disc clamp for securing the discs to a spindle motor is disclosed in co-pending U.S. patent application 07/893,490. In such a disc clamp, a contact area is circumferentially formed about the outer diameter of the disc clamp. This contact area is displaced out-of-plane from the remainder of the disc clamp in the direction intended to be toward the discs when the clamp is installed, and a plurality of screws, disposed radially inward from the contact area, attach the inner portion of the disc clamp to the spindle motor hub. In this manner, the juncture of the contact area and the unformed center of the disc clamp acts as a spring mechanism to clamp the inner diameter of the discs in place.
A problem arises with the use of this type of disc clamp, however, when the above noted disc thickness and clamping forces are considered. Since the disc clamp is secured with a plurality of screws circumferentially spaced about the periphery of the disc clamp, the majority of the clamping force is exerted at the location of the screws, with a substantially lesser force applied to the discs in those areas between the screws. This variation in clamping force can cause the discs themselves to be mechanically distorted in a manner sometimes referred to as "potato chipping", meaning that the areas of the discs adjacent the disc clamp screws are displaced further from the disc clamp than the areas of the discs between the screws.
Distortion of the discs from an ideal flat condition leads to undesirable modulation of the read/write signals detected and produced by the heads of the disc drive. That is, since the heads will fly at varying heights about the circumference of the disc when attempting to follow a distorted disc, the signals used to write and read data on the discs may be inadequate to ensure reliable data storage and recovery.
It would therefore be desirable to develop a mechanism which would aid in more evenly distributing the clamping force of the disc clamp about the inner diameter of the discs, thus reducing distortion of the discs and minimizing undesirable data signal modulation.